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One surprising finding I'm having from taking CO2 readings in various places is that I'm consistently getting readings between 700 and 800 ppm at supermarkets.

I mostly took readings at peak hours. I'll need to go back at off peak times to see how much the readings change. I was really amazed at how "not terrible" the reading at Trader Joe's was.

Picture 1: Trader Joes at noon on a Saturday. It is packed. It was a total surprise to see CO2 readings between 700 and 800ppm! (Fair)

Picture 2: Smart and Final, a mostly California-bases grocery outlet selling a mix of regular groceries and bulk package items with a reading of 714ppm. (Good)

Picture 3: Walgreens Pharmacy, at off peak hours. 529ppm. This is very good, but hard to believe. I'll have to go take this again.

Picture 4: Nob Hill Foods, a small grocery chain in Northern California. 726ppm. Good-Fair.

I'm making some blunt assumptions about what these readings mean. From what I've been gathering from scientists posting about air quality readings, 400ppm is a baseline and every +200ppm gets you from excellent to good to fair to unhealthy.

Most people seem to be suggesting 800 and below as the line to really start exercising more strict caution if you're trying to avoid infection.

But keep in mind that's based on 400ppm as the baseline. My baseline for some of these readings is shown in the attached photo. It's 470ppm outdoors on that day.

My baseline is likely higher because I'm in an urban area at a mall near very busy roads. There's a lot of extra ambient CO2 so my cutoff lines would be 670 and below (excellent), 870 and below (good), 1070 and below (fair).

Every 400ppm above baseline roughly equates to 1% of the air you breathe being exhaled by someone else. That's like getting mouth to mouth once every 6-8 mins.

Want to see what a CO2 chart for an office meeting with about 12 people for one hour looks like? We start with excellent indoor air quality at 9am with 500ppm of CO2.

After one hour in a poorly ventilated space, the CO2 readings are 1720ppm! And this is a fairly spacious office that would have a bit of air reservoir to slow down the rise in CO2 levels.

Yikes! This means everyone is breathing quite a bit out of each other's lungs. If you're only going to wear a mask in the riskiest situations, this should be one of them.

Keep in mind that just having high CO2 concentrations doesn't mean much unless someone is contagious in the room, but if there was someone contagious that day, lots of people in that meeting would have gotten whatever was being passed into the air be it Covid, flu, RSV, or a cold.

I'm sharing all of this with you because we could still be in for another wave and lots of people have waned immunity and prior infection isn't good at keeping you from getting a next infection.

It's also because I'm realizing among my real world friends that some are still focusing on hand washing to avoid getting Covid.

They're also trading lower risk activities for higher risk ones because they don't understand how it works. My friends who do catering told me they were catering huge house parties every day during the height of the pandemic when restaurants were closed for dine-in.

Restaurants have modern HVAC systems and have to pass building inspections. I've been surprised that readings in most restaurants are quite good (off peak at least). Very few homes will have ventilation systems like those in even a run down restaurant.

Going to a house party instead of meeting at a restaurant is a bad trade-off!

I spent some time inside a variety of food/retail businesses this week as a photographer. Here's an #Aranet4 #CO2 reading from a bakery where the owner is very Covid conscious. She keeps it very well ventilated. This small bakery cafe was at full capacity with 15+ people. The CO2 reading was 471ppm against an outside reading of 415ppm.

Front door open w/commercial kitchen in the back pumping air. That it was windy also helped.

Also took a reading deep in a packed small Thai restaurant w/Covid aware owner. 550ppm, door open + all windows 1/4 open. Very surprised it was that low.

I've yet to measure a restaurant exceeding 800ppm (which is roughly 1% of re-breathed air per breath).

I may eventually feel just fine dining indoors in some places once we have some more clarity with the direction that #Covid & therapies are heading. On the flip side, there are types of places that often have bad airflow that I'm never looking at the same again.

My last 2 eye clinics both hit 1000ppm.

Some math for those who aren’t familiar with the numbers. 420ppm is the baseline. Every 400 above that represents 1% of rebreathed air per breath.

Average person breathes about 15x a minute. At 820ppm (1% rebreathed), it takes about 7 minutes for you to take a lungful of secondhand air. At 1220ppm (2% rebreathed) it’s closer to 3 minutes.

HEPA filters can mitigate risk and clean the air, but some research at Bristol University recently showed why fresh air is still important. They found that the Covid virus dies 4x faster in less acidic environments. Exhaled breath is acidic so the more exhaled breath trapped in with you, the more acidic the air around you becomes.

Fresh air is not acidic and not as friendly to sustaining Covid (and possibly other respiratory viruses too).

https://www.bristol.ac.uk/news/2023/june/airborne-viruses.html

@jeridansky I'm wearing a mask for the forseeable future too. I decided to start doing this to gather data points to help me decide how to navigate the next phase of the pandemic and (hopefully) eventually to fewer precautions.

I've been most pleasantly surprised readings were so low in the restaurants that I've gotten takeout orders from, but I guess I shouldn't be too surprised once I think about it. Kitchens are inherently messy and smelly so even before we consider that they have to pass HVAC inspections, every restaurant's air flow is already being influenced by the needs of the kitchen.

It's not going to be this year, but I have hope that I'll be able to go enjoy a restaurant again.

What kind of readings are you seeing at grocery and drug stores?

@sysop408 I haven't checked recently, but I was getting 490-610 at the drugstores, 633 at the grocery store. Also 692 at the Apple store!

I get great readings at my dentist and periodontist because I've trained them to open the window in the room I'll be in. (I'm fortunate that they are both in buildings with windows that open.)

@mvilain I got the Aranet4 on Amazon. It's pretty much the top of the line one for consumer use and it's pricey ($200-$250 US). There are cheaper ones that are still accurate, but have some drawbacks and poor battery life.

Yeah schools... Ugh. I know several people who only took basic precautions and still never got Covid until their kids brought it home.

I don't have kids, but see @surfingreg's post below where he says that he sampled his kid's brand new school at 1500ppm daily (almost 3% of rebreathed air per breath).

I can understand old buildings, but we gotta do better with our new buildings.

https://fosstodon.org/@surfingreg/110846804578262167

@sysop408 @surfingreg

Oy. After I posted, I did an Amazon search and saw an Aranet4 for $215. That's the price of a good 4-6TB hard drive. So much for that idle thought.

I find it interesting that @pluralistic quit smoking a while ago after he realized he was literally burning through 2-3 laptops per year.

@mvilain take a look at the Vitalight Mini if you want something inexpensive, but accurate with some drawbacks. It has the same type of premium sensor that's in the Aranet4, but its operation and battery life leave much to be desired.

The Aranet4's price changes a lot. I got mine for $185. It was originally $150 before it became popular. Now it seems to be anywhere between $180 and $250 depending on when you buy it.

Here's a guy in New Zealand who did some great reviews comparing CO2 monitors.

https://breathesafeair.com/air-quality-monitor-reviews/

@surfingreg